1. Field of the Invention
The present invention relates to a memory device and a semiconductor device including the memory device.
2. Description of the Related Art
In portable electronic devices such as a mobile phone, a smartphone, and an e-book reader, a semiconductor memory device (hereinafter, also simply referred to as a memory device) such as static random access memory (SRAM) or dynamic random access memory (DRAM), which writes and reads data at high speed, is used so as to store image data temporarily. In order to increase operation speed of the memory device, in the case of SRAM, it is effective to increase switching speed of transistors by miniaturization because data is stored with the use of flip-flops including a plurality of transistors. However, in the case of DRAM, data is stored by supply of electric charge to a capacitor; accordingly, an increase in switching speed of a transistor controlling supply of electric charge is not greatly effective to operation speed in writing and reading data.
Patent Document 1 discloses a semiconductor memory device in which two word lines are connected to each other at a word line parallel connecting point to reduce wiring resistance from that of a conventional circuit, so that delay in word lines is solved.